Get ready to pucker up, Rupert Grint — the upcoming open casting call for "Harry Potter and the Half-Blood Prince" is about to become your own personal casting couch (albeit in a PG-13 world).

In the next installment of the series, due in November 2008, Grint's Ron Weasley gets a girlfriend — or, more accurately, a make-out partner — in the form of Lavender Brown. So to make sure Ron gets just the right shade of Lavender, director David Yates has a little test in mind.

"You know what I'm going to do?" Yates said. "I never did this before, but I'm going to get Rupert together with the top five Lavenders, get him to come and read with them and snog with them. It's a chemical thing, and you want to feel that chemistry between them. That will help me decide."

"Really?" Grint asked — since this was news to him. "Oh, wow, I didn't realize that. That's going to be interesting. It's going to be embarrassing."

Grint already had his first on-screen kiss in the indie film "Driving Lessons" (see "Rupert Grint Learns Driving, Making Out — But Not At Hogwarts"). Still, even with that notch in his belt, the actor isn't any more at ease with the idea of being instructed at how to tilt his head at just the right angle for the cameras to get the most of his mouth. "It is a bit clinical and they do so many takes," Grint said. "I'm not really looking forward to it."

Even though Yates has already seen a lot of Lavenders, he's eager to test the waters with an open call July 1 in London because of the success they had last time around with finding Evanna Lynch, who plays Luna Lovegood in "Harry Potter and the Order of the Phoenix," which is in theaters July 11. Though they had a few potential Lunas who were "very, very close" the last time around, as they do with the Lavenders now, the filmmakers decided to throw the auditions open just to be sure.

"We had the biggest, maddest auditions you've ever seen," Yates said. "Something like 18,000 kids turned up, and when I pulled up in the car and looked out the window, the queue went around and around the block. But we found Evanna in that mix, so it was worth it."

There will also be an open casting call in London on July 8 for the role of Tom Riddle. Though the teenage form of Lord Voldemort was seen before in 2002's "Chamber of Secrets," the actor who played him then, the nearly 30-year-old Christian Coulson, has aged out of the part. "I think Christian's a brilliant actor, and I thought it was a terrific piece of casting, but he's too old now," Yates said.

Like Lavender, the filmmakers have seen a few candidates so far over the past few weeks but want to find just the perfect person for the part — even if he doesn't look exactly like his predecessor.

"What I want is that quality of spirit," Yates said. "Someone who is odd, charismatic, cool, has a quite cold spirit which Voldemort embodies. If I find that, that's the most important thing."